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ELEC1130 - Circuit Analysis and Design > Basic Electronics > Flashcards

Flashcards in Basic Electronics Deck (57)
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What is the equation for a Thevenin equivalent circuit?

Rthevenin = Vopencircuit / Ishortcircuit


What is Voc?

> The voltage between A and B when there is no current flowing between A and B
> Open Circuit


What is Isc?

> The current flowing between A and B when the circuit is closed
> Short Circuit


How can Rthevenin be calculated without Voc and Isc?

If the voltage source is turned down then a multimeter in resistance mode could be used


What is the equation for frequency of an AC circuit?

F = 1/T


What is the equation for radian frequency?

ω = 2πf


What are the equations for voltage of an AC circuit?

v = ASin(ωt)
v = v0 × Sin(ωt)
v = Voltage
A = Amplitude
v0 = Peak voltage
ω = Radian frequency
t = Time


What is the equation for current of an AC circuit?

I = (V/R)Sin(ωt)


What are 4 equations for power?

P = IV
P = QV/T
P = V^2/R
P = E / T


What is the most important equation for voltage?

V = IR


What is the inverse of resistance? What is the symbol?

> Conductance
> Symbol: G


What is the equation for conductance?

G = 1/R


What is an equation for current in terms of conductance?

I = VG


What are 2 equations to find the EMF of a battery?

Vemf = I (Rint + Rload)
Vemf = Vpd + I×Rload


What is the equation for the charge stored in a capacitor?

Q = CV


What is an equation for the current through a capacitor?

I = C×(dV/dt)


What is an equation for the voltage across a capacitor over a period after a period of time?

V = (1/C)∫ I dt


What is an equation for the energy stored in a capacitor?

E = 1/2CV^2


What is the equation for capacitors in series?

1/Ct = 1/C1 + 1/C2 + 1/C3 +...+ 1/Cn


What is the equations for capacitors in parallel?

Ct = C1 + C2


What is KVL?

> Kirchoff's voltage law
> Sums of the voltages taken around any loop is equal to zero.
> Sum EMF's = Sum PD's


What is KCL?

> Kirchoffs current law
> Sum of currents entering a node equal zero
> Sum of currents into node = sum of currents out of node


What is an ideal voltage source?

It is a voltage source with no internal resistance


What is DC voltage?

Difference in electrical potential between two points in a circuit


What is AC voltage?

The Root mean squared voltage between two points on a circuit


What is root mean squared voltage with regards to AC circuits? How is it calculated?

AC circuits are given a RMS voltage which is the average voltage. The voltage can be higher and much lower (negative) than the RMS voltage.
To calculate the RMS voltage:
> Square all values off the voltage over a period of time
> Find the mean average of all the values
> Square root the mean average


What is the voltage of batteries in series?

The sum of the voltage of all the batteries (taking into account polarity)


What is the symbol for an ideal DC voltage?

A circle with a + and - at each terminal


What is the symbol for an ideal AC voltage source?

A circle with a sine wave in the middle


What is the voltage divider equations?

Vout = Vin × R2/(R1+R2)


What is a current divider?

This is when there are two resistors in parallel. Each resistor has a different current through it dependent on the resistance of the resistor in that branch


What are the equations for the current divider?

Is = I1 + I2
Is = (G1 + G2)V
I1 = G1V
I2 = G2V
I2 = Is×R1/(R1+R2)
[Not similar to voltage devider!!!!]
I2 = Is×G2/(G1+G2)


What is the equation for DC current?

I = Q/T


What is the equation for AC current?

I = (d/dt)q


How is the current from batteries increased?

> By combining them in parrallel
> They are summed together


What is an ideal current source?

A current source with infinite resistance.


What is transient analysis?

This is the analysis or a circuit over time


What is the equation for the transient analysis of a capacitor discharging through a resistor?

0 = IR + (1/C)∫I dt


Describe what happens as a capacitor is charged over time when there is a resistor in the circuit

> At the start the voltage across the capacitor is zero and so (because of KVL) all the voltage from the battery is across the resistor
> As more charge is stored on the capacitor, its potential difference increases (Q = CV)
> Due to KVL the EMF of the battery is equal to the sum of the potential differences in the circuit so as the voltage across the resistor decreases as the capacitor becomes charged
> Eventually the capacitor has the same PD as the battery and so the voltage across the resistor is zero. At the this point there is no current


What is the equation for reactance?

Xc = 1 / ωc


What is the unit of reactance?



What is reactance dependent on?

> Frequency
> capacitance


When a capacitor is placed in an AC circuit, what is the equation for the current through the capacitor?

I = C(dV/dt)


What is the chain of equations to calculate the current through a resistor at any point of time when the capacitor is in an AC circuit?

I = C(dV/dt) => I/C = dV/dt
V = V0sin(ωt) => dV/dt = V0ωcos(ωt)
I/C = V0ωcos(ωt) => I = V0ωCcos(ωt)
I = V0ωCsin(ωt + π/2)


What is the resistance of a diode in the forward bias direction?

> Ideally: 0Ω
> In real life it is very small


What is the resistance of a diode in the reverse bias direction?

> Ideally: ∞Ω
> In real life it is very high


Do diodes follow ohms law?



What is a threshold voltage?

Diodes have a minimum voltage above which the resistance is very low but below the threshold voltage the resistance is high. Diodes are non ideal.


What is a common use of a diode?

Used in rectifiers


For a power source and variable load, When is maximum power dissipated by the load? What are the two (sort of ) proofs for this?

> Max power is dissipated by the load when it is equal to the internal resistance of the power source
> Load = 0Ω
- So the voltage across it is 0
- P = 0^2/0 = 0
- Power dissipated = 0
> Load = ∞Ω
- So the Current through the resistor is 0
- P = 0 × V = 0


What is a FET? When thinking about equations what can you imagine it as?

> A Field effect transistor
> imagine it as a electrically controlled variable potentiometer / switch (it can turn on and off and also allow certain amounts of current through)


In a FET amplifier, what is the use fo the capacitors on the input and output? Explain

To remove the DC bias
This allows the input and output to only oscillate around 0V and not be translated to oscillate around a higher / lower voltage


What are the 3 pins on a FET?



How does a FET amplifier work?

The input voltage varies the amount of current allowed through the FET (essentially changing its resistance) this then diverts current from the output and so this allows the output voltage to be amplified


What is Vdd?

Supplied voltage for the output of the FET amplifier circuit


What is Vds?

The voltage across the FET from drain to source


What is Rd?

This the resistor used to bias the circuit